Breastfeeding and Baby Constipation

Hi everyone, I just gave birth 5 days ago and I'm getting a bit worried with breastfeeding. When I was in the hospital, he was latching perfectly and I did not a problem nursing. My milk started coming in and that completely stopped. I pump now (every 2 hours and I dont drain the breast) and that has relieved some of the pain, but he will not latch and I can only feed him via syringe. I'm afraid to use a bottle bc I don't want him used to that nipple and never take mine, but I'm now worried he is only used to being fed by syringe. I have to feed him though so I try to breastfeed first, and when that doesn't work, I pump and use the syringe.

I also think he is constipated and I don't know what to do to fix it. He hasn't pooed in 2 days, and though I see him straining, nothing comes out. I'm currently bicycling his legs and massaging his bum.

He has his first appt with the pediatrician tomorrow but hoping I can get some advice before then.

Motherhood!

Thanks for any help!